There is a substantial time gap between when parents develop concerns about their child (ages 1–2) and when they receive a diagnosis of autism (ages 3–5), delaying the onset of critical interventions. Few studies have examined how the timing, type, and quantity of early parental concerns are associated with age of diagnosis. The aims of this study were to describe characteristics of parents’ concerns in a large community-based sample and explore how characteristics of concerns relate to age of diagnosis. This study included 853 parents of 2- to 5-year-old children with an autism diagnosis. Parents completed an online survey including questions regarding their child’s age when they first became concerned about their development, what their first concern was, all concerns they have had about their child, and age of diagnosis. An earlier age at first concern and the presence of several specific types of concerns (i.e., delayed/absence response to name, reduced eye contact, developmental regression, delayed gesture development, limited emotional response) were found to be significant predictors of earlier age at diagnosis. In addition, when accounting for age of first concern and the presence of specific types of concerns, a higher number of concerns was associated with a later age of diagnosis. Several specific types of concerns significantly predict the age at diagnosis, although several of these specific types are not commonly reported by parents. Educating parents and pediatricians about these concerns may improve early detection and intervention, ultimately improving long-term outcomes for children and families.